1. Field of the Invention
The present invention relates to a printed coil substrate for an optical disc actuator, an optical disc pickup, and an optical disc drive device.
2. Description of the Related Art
An optical disc pickup is equipped on an optical disc drive device, and an optical disc actuator is equipped on the optical disc pickup. In the optical disc actuator, in order to drive a movable portion having an objective lens relatively to a fixed portion, a magnet is equipped on one of the movable portion and the fixed portion, and an electromagnetic coil is equipped on the other. The electromagnetic coil is attracted and repelled by the magnet by magnetic flux generated when a current is made to flow, and the movable portion is driven relatively to the fixed portion. Note that the fixed portion itself is linearly driven in a radial direction of an optical disc. Thus, a surface of the optical disc can be scanned because the fixed portion is linearly driven in the radial direction while the optical disc is rotary driven.
The electromagnetic coil can be formed of a wire coil or a printed coil substrate, which is made by forming a coil pattern on a flexible substrate.
In the optical disc actuator, the movable portion is held at a neutral position in terms of design so that magnetic force from the magnet (permanent magnet) can be obtained the most. When the movable portion is shifted (moved) in a focal direction or a tracking direction from the neutral position, an effective part of the coil, which generates a driving force, is also shifted. Therefore, sensitivity is deteriorated and recording and reproducing performance are negatively affected. Note that the sensitivity is a general term of accuracy for moving the movable portion to an appropriate position based on attraction force and repulsive force generated when an electric current is applied to the coil of the movable portion in the magnetic flux of the magnet.
In particular, in an actuator formed of the printed coil, wiring for wires or intermediate substrates and through holes for other layers should be provided on the flexible substrate in addition to the coil pattern. Therefore, it is difficult to widely provide the effective part of the coil on a surface opposite to the magnet so that the deterioration of sensitivity is suppressed compared to the actuator formed of the conventional wire coil. In addition, in order to obtain the same performance as the wire coil, the printed coil itself should be large, and therefore the actuator should be large and an optical pickup on which the actuator is mounted should be large. Furthermore, since the size of the printed coil itself affects a quantity obtainable from a base material, if the size of the printed coil itself becomes large, the quantity obtainable from the base material is reduced and manufacturing cost is increased.
As the conventional printed coil substrate, Patent documents 1 to 5 are known.
In Patent document 1, in each layer of a first layer and a second layer of a printed coil substrate of two-layer constitution, magnitude of a coil pattern of the most outer layer (first layer) provided with a land part and that of a coil pattern of an adjacent layer (second layer) are changed. In the coil pattern of the layer having the land part, width (vertical direction) is made small so as not to overlap with the land part in the same layer.
In Patent document 2, in a plurality of printed coil substrates, pattern width of a coil pattern formed in a layer near a magnet is made narrower than the pattern width of the coil pattern formed in a layer far from the magnet.
In Patent document 3, a plurality of printed substrates on which a focusing coil and a tracking coil are formed as a circuit pattern are laminated so that the focusing coil and the tracking coil are not overlapped in a thickness direction of the printed substrates.
In Patent document 4, each of coil elements is composed of a circuit pattern formed on a printed substrate, shapes of the circuit pattern are different in each phase, and a length of an effective conductive part contributing to a driving force of the coil is set shorter in an effective coil close to the magnet than others.
In Patent document 5, coil patterns formed on printed coil substrates are made different depending on each layer. In other words, the coil patterns having different shapes are used and a relative position relation is made different.
Patent document 1: Japanese Patent Application Laid-Open No. 2005-166219
Patent document 2: Japanese Patent Application Laid-Open No. 2007-080305
Patent document 3: Japanese Patent Application Laid-Open No. H07-093778
Patent document 4: Japanese Patent Application Laid-Open No. H07-210884
Patent document 5: Japanese Patent Application Laid-Open No. 2006-040415